A Breastwork is a fortification. The term is usually applied to temporary fortifications, often an earthwork thrown up to breast height to provide protection to defenders firing over it from a standing position. A more permanent structure, normally in stone, would be described as a parapet. Table of Fortification, from the 1728 Cyclopaedia. ... A parapet consists of a dwarf wall along the edge of a roof, or round a lead flat, terrace walk, etc. ...